Recently, in the field of optics, magnetic recording, and precision processing, there is a demand for a displacement element capable of adjusting the length and position of an optical path by orders of submicron. In an attempt to satisfy such a demand, developments have been pursued for a displacement element which utilizes a displacement generated by an inverse piezo-electric effect and an electrostrictive effect obtained when a voltage is applied to a piezo-electric/electrostrictive material (for example, ferroelectric substances and the like).
As a conventional displacement element such as described above, Japanese Unexamined Patent Publication No. 10-136665 discloses a piezo-electric actuator having a structure where a piezo-electric/electrostrictive material is formed into a plate-like body which is then perforated, thereby integrally forming a fixing section, movable sections, and a beam section for supporting them into one-piece unit, and an electrode layer is formed in the beam section. In this piezo-electric/electrostrictive actuator, when a voltage is applied to the electrode layer, the beam section shrinks in a direction that connects the fixing section to the movable sections due to the inverse piezo-electric effect and electrostrictive effect. As a result, the movable sections can be displaced along an arc or rotatively displaced within the surface of the plate-like body.
Japanese Unexamined Patent Publication No. 63-64640 discloses a technique using an actuator with a bimorph. The electrode of the bimorph is divided into a plurality of electrodes, and the divided electrodes are selectively driven. In this manner, positioning can be performed with high accuracy at high speed. This prior art publication shows (in particular, in FIG. 4) the structure where two bimorphs are positioned in an opposed relation to each other.
However, the conventional actuators described above are entirely constituted by fragile materials which are relatively heavy in weight. Therefore, they have low mechanical strength, and are poor in handling characteristics and impact resistance.
Conventionally, in an attempt to improve the mechanical strength of the conventional actuators, the strength of the section easy to vibrate has been enhanced. For this purpose, the enhancement in the rigidity of the vibration section has been conducted. The enhancement adversely affects the basic properties of the actuator itself, such as resonance characteristics and displacement, and causes a problem in that the adjustment of the basic properties becomes difficult.